Diversidade de espécies e variabilidade genética de Begomovírus infectando Cansanção (Cnidoscolus urens L.) no Estado de Alagoas

Abstract

Diseases caused by begomoviruses (family Geminiviridae) are a serious constraint to cultivated plants in tropical and subtropical regions of the world, including Brazil. Begomoviruses are also associated with a wide range of weeds, which are considered to be begomovirus reservoir as well as primary inoculum sources for epidemics in crops. We have carried out a survey of the weed Cnidocolus urens (family Euphorbiaceae) in the state of Alagoas. A total of 34 samples showing typical symptoms of viral infection were collected in four different areas of the Alagoas state. Total DNA was extracted from each sample and complete viral genomes were amplified using the DNA polymerase from phage phi29, cloned into plasmid vectors and completely sequenced. A total of 21 clones we obtained (19 DNA-A and 2 DNA-B). Pairwise sequence comparisons and phylogenetic analysis indicated the presence of two new begomovirus species whose proposed names are: Cnidoscolus mosaic leaf deformation virus (CnMLDV) and Cnidoscolus severe rugose virus (CnSRV). The two new species were more related to Passionfruit severe leaf distortion virus (PSLDV, FJ972767) isolate from the Bahia state, Brazil. The DNA-A of the two new species had a typical bipartite New World begomovirus genome organization and displayed < 87% sequence identity each other. Evidence of recombination was found among isolates of CnMLDV and CnSRV. The recombination events were detected in the CP, Rep and REn genes, having CnMLDV and PSLDV as the putative parents. Analysis of the CnMLDV population demonstrated that its genetic variability is very high. dN/dS values indicated that the CnMLDV population may be under the influence of purifying selection or has undergone a recent expansion, so that the occurrence of mutations is not sufficient to fully explain its genetic variability. It is concluded that recombination, as well as mutation, are important evolutionary mechanisms acting on genetic variability of the CnMLDV population. The findings of this study indicate that C. urens can play a significant role, both as inoculum source and as source of emerging novel viruses.